Ionic sieving through Ti₃C₂(OH)₂ MXene: First-principles calculations

Recent experiments revealed a great potential of MXene nanosheets for water desalination applications as ultrathin, high-flux, and size/charge-selective sieving membranes. Here, we conduct first-principles density functional theory calculations to explore possible mechanisms for the charge-selective ionic transport through Ti₃C₂(OH)₂ MXene. We find that the charge selectivity originates from the charged nature of the MXene layers. For example, due to the electrostatic interactions, ions of different charge states have different energy barriers for the intercalation between the MXene layers. In addition, the system shows dynamic response to the intercalating ions, even in their hydrated states, by changing the interlayer spacing. Our findings highlight the importance of membrane surface charges on the ion sieving performance.